If you have a enterprise email and they have calendar's that you can share/sync/etc..that's why you get that...you can get the default back by either deleting the service books that say "ICAL" for the email accounts you have...or change the calendar color of your email accounts to something other than blue (that worked for me)...

Yep, remove the email accounts or service books and the calendar events will default to the device default calendar... I would then sync it with Outlook then add the email account back in a sync again.